Implement Decorators

[S-YOU]

This is for #72, but I guess this implementation may be more a like a hack, because Instead of generating Go code, I triggered AST to add more nodes while walking through.

• Confirmed simple decorators working, not sure there is some complex use cases.
• This is only for function decorators, class decorators not yet supported.
  (I don't get this syntax for class working yet. C = decorator(C))

% make run
def bold(fn):
    def wrapped():
        return "<b>" + fn() + "</b>"
    return wrapped

def italic(fn):
    def wrapped():
        return "<i>" + fn() + "</i>"
    return wrapped

@bold
@italic
def hello():
    return "hello world"

print hello()

<b><i>hello world</i></b>

import contextlib

@contextlib.contextmanager
def tag(name):
    print "<%s>" % name
    yield
    print "</%s>" % name

with tag("h1"):
  print "foo"

<h1>
foo
</h1>

[trotterdylan]

Thanks for doing this! Comprehensions and generator expressions work this way so there is precedent for the approach. I like how neat and tidy it is. Good work!

I was trying to figure out if this will work with decorators that take arguments. I think it does, but just want to confirm. It would be good to have some test cases for that.

[trotterdylan]

slightly shorter:

def bold(fn):
  return lambda: '<b>' + fn() + '</b>'

[S-YOU]

Sorry for late update, updated those. Hopefully CI is ok.

[trotterdylan]

Great! Thanks for the update. Will merge shortly.